The present invention relates a photometer capable of displaying difference between a couple of measured values.
Generally, in taking pictures, a photometer capable of displaying a difference between measured light values of two arbitrary spots on an object field is required especially when a photographer wants the whole object to exist within the effective exposure range of a film.
As a photometer of the type, U.S. Pat. Nos. 4,309,090 and 4,396,263 disclose exposure display devices which are adapted to display a difference between a measured value of a comparatively wide area and that of a comparatively narrow area. The difference value to be displayed by such devices is obtained by two independent photometry means; one for the comparatively wide area and the other for the comparatively narrow area.
Equipping a photometer with two photometry devices as seen in the above conventional photometers, however, causes disadvantages such as complication of the photometer, increase in cost, inconvenience in the use, and so on.
In addition to the above described photometers, a flash meter adapted to display a ratio of flashlight components to ambient light components has been proposed. In taking pictures, it is very important to know the ratio of the flashlight to the ambient light, because, if these lights to illuminate an object are different from each other in light characteristics, it is required to know a possible final image in advance before taking pictures. Especially in the case that the ambient light is of a tungsten lamp, it is essential. The color temperature of the tungsten light is relatively low with respect to a film suitable for light of a day light type, and so, the color tone of the final image becomes more reddish in proportion to the amount of the tungsten light components. On the contrary, the final image has a more natural color tone as the flashlight components increase. This is why it is necessary to know the ratio of the amount of the ambient light components to the total light amount in advance. Then, that ratio may be adjusted according to a photographer's intent so that the reddish tone may be emphasized or weakened.
The above described conventional flash meter is adapted to display simultaneously a first dot indicating the total amount of the flashlight components and the ambient light components, a second dot indicating the amount of the flashlight components, and a third dot indicating the amount of the ambient light components on an analog scale. Due to the simultaneous display of those amounts, some users unfamiliar with such a flash meter could not read the scale easily. Then, from the point of view of facilitating the reading of data, it can be considered that the realization of displaying by digits the difference between the measured value of light coming from an object in the flash containing the ambient light and that in only the ambient light for the numerical representation of the efficiency of the flash will allow users to know easily and quantitatively that a greater difference value indicates a more natural tone and a smaller one indicates a more reddish tone inherent in the tungsten lamp.